Theodolites are a type of optical instrument used for measuring precise horizontal and vertical angles. They are often used by land surveyors for determining potential building dimensions and property boundaries when sighting vacant land. They are also used extensively in the construction and engineering industries to layout building foundations and walls, leveling of lots and grade work, mapping out roadways, bridges and other infrastructure construction and other large-scale construction projects.
Theodolites consist of an optical sighting scope in a fork-mounted design that allows the scope to rotate freely around both the horizontal and vertical axes. Crosshairs located within the scope are used to sight and align the object being measured. Bubble levels are used for the proper leveling of the instrument.
There are two different ways theodolites measure the angles, by using graduated setting circles or by using internal optical scales and digital readouts. Digital-based theodolites are far more common, easier to use and more accurate than using graduated setting circles. Angles measured with digital theodolites can achieve accuracies down to a few seconds of arc.
Many theodolites today are known as ‘Total Stations’ where the instruments can measure the angles electronically. The digital information is stored in memory and the instrument can use the basic angle information to calculate distances from the instrument to a specific point and perform automatic triangulation calculations.
As with all precision measuring instruments, theodolites cannot perform accurate measurements unless they are calibrated periodically. At a typical construction site, Theodolites are subject to hazardous working conditions from temperature extremes, excessive vibrations from other construction equipment and they are often bumped or even dropped when being transported to the site.
Theodolites that are used frequently or if they have not been used for a significant amount of time can show measurement errors. Due to the high accuracy of theodolites, it will not be obvious to the user if the instrument is not reading correctly.
The proper calibration of theodolites can be performed in various ways. The actual procedure and equipment required for the calibration will depend on the type of the theodolite and the accuracies required.
In addition to the horizontal and vertical angle measurement accuracies, the proper calibration of a theodolite also involves checking the instrument’s leveling bubbles, crosshair alignment, and the runout of the horizontal and vertical travel. The instrument will also be cleaned and any broken or worn parts will be repaired or replaced.
can calibrate many types of theodolites and other optical equipment in our ISO/IEC 17025 accredited calibration laboratory. For more information on our equipment calibration capabilities, contact e2b calibration.